----- Original Message ----- From: "Steven M. Bellovin" <[EMAIL PROTECTED]> I'm > forced to conclude that we have two choices: either we give up on flow > labels entirely, or we permit them to be modified en route. >
There is a third option, which is consistent with the way flow labels are embodied in the running code (remember that notion? running code) In the IPv6 running code, the flow labels don't really exist. This is very much like the way Unix had non-existent bits to the left of a char. The getchar function was then able to read a char and detect EOF, even though there was no EOF char. Many people have used the following code ...while((c=getchar()) != EOF)....and still assume the char is 8 bits. They do not spend their time running around trying to police what is in the bits to the left of those 8 bits. With IPv6++, the 20 bits have a 4 bit in-header data length value. The other 16 bits have a unified StarGate value. Routing is only done on the left-most 64 bits of the Source and Destination fields. Depending on the Protocol field (NXTHDR), the protocol designer is able to define how the 4 bit length, 16 bit StarGate and 16 data bytes are defined/used, etc. Just as with the EOF, that may be totally outside of the user's view. As one example, the VPC protocol can ride inside of the header. That allows for remote downloading and control of the protocol engine. The program running in the protocol engine, then defines how the other bits in the packets are processed. The 20 bits and 16 bytes used by VPC are in another dimension from the user's information. That dimension is best left out of the view of the users, just like the EOF bits. http://www.dot-biz.com/INFO/Papers/VPC In summary, forget about the 20 bit flow label. Just imagine it is not there. Jim Fleming 2002:[IPv4]:000X:03DB http://www.IPv8.info http://www.dot-biz.com/INFO/Papers/ -------------------------------------------------------------------- IETF IPng Working Group Mailing List IPng Home Page: http://playground.sun.com/ipng FTP archive: ftp://playground.sun.com/pub/ipng Direct all administrative requests to [EMAIL PROTECTED] --------------------------------------------------------------------
